The invention relates to a chip card, preferably a contactless chip card.
DE 42 05 556 C2 discloses a chip card with electronic elements for a contact-free exchange of data by means of electromagnetic alternating fields, using an external apparatus. The chip card incorporates one or more switches which can be manually operated and allow the electronics or parts of the electronics to be manually switched on or off so as to release data and characteristics of the chip card only in accordance with the options of the user of the chip card. This should render the unauthorized identification of the chip card more difficult. In addition to a definitive blocking of the chip card, the activation of this card by the switches in the plastic card is possible in emergency situations. The switches, embedded in the card material, may be formed as toggle switches in that two recognizable marks on the upper surface of the card disclose the switching position.
Such a mechanical switch is, however, very elaborate from a manufacturing point of view and, in operation, it is sensitive to disturbances.
The international publication WO 98/20450 discloses an identification card with a transaction coil and a method of manufacturing this card. The transaction coil is formed as a silver or generally conductive paste silk screen component which is incorporated in a plastic card body corresponding to the conventional ISO standards and whose ends are subsequently bared by means of a milling process for implanting a special chip module, or whose contact ends have already been kept free in a lamination or injection-molding process, and whose contacting can only be realized by intentionally exerting pressure and becomes automatically inactive after ending this pressure.
Such a touchlessly functioning identification card should provide the possibility of intentionally bringing about the process of identification and transaction of data. The deliberate switching of a transponder coil is essential in this case. However, this identification card is also very elaborate as regards its manufacture and, in operation, it is sensitive to disturbances.
An electronic card with a function which can be manually activated is known from FR 2,728,710-A1. This electronic card has a plastic body which comprises the function components that are fed from the battery. The battery is connected to a sensor whose physical properties vary due to its manual operation. An electronic circuit monitors the operation of the function components independently of the state of the sensor. A resistance strain gauge may be used as a sensor which reacts to bending of the card, or a thermistor may be used which responds to the warmth of a user""s finger touching the card. The sensor may also comprise pairs of electrodes between which the resistance changes upon a user""s touch. For a reliable operation, the function components should only be activated when the rate of change of the physical property detected by the sensor is within a predetermined range.
Such sensors have proved to be unreliable. For example, the responses of a thermistor or a thermoelement or the resistor between two electrodes may be dependent on the temperature of the user""s finger or on the fact whether the user wears gloves.
It is an object of the invention to form a chip card in such a way that an arrangement is obtained with little manufacturing effort, ensuring a reliable activation or deactivation of the chip card by the user.
According to the invention, this object is solved by a chip card, preferably a contactless chip card, comprising a data-processing circuit for receiving, processing and/or transmitting data signals, and at least a capacitive switching element which can be activated by means of a user""s touch, whose activation of the switching element triggers at least the transmission of data signals from the data-processing circuit and without whose activation at least the transmission of data signals from the data-processing circuit is prevented.
A cost-efficient, reliable switching possibility is provided by forming capacitive switching elements for activating or deactivating the chip card. A chip card thus formed is robust and suitable for high-stress use. Erroneous activation by, for example, forgetting a switch in an unwanted switching position is excluded. The capacitive switching elements used in accordance with the invention are insensitive to dirt, oxidation, humidity or to the user wearing gloves. The capacitive switching elements formed in accordance with the invention can be manufactured at minimal cost and with a minor additional manufacturing effort. The switching elements formed in accordance with the invention are not subject to any mechanical wear. Inadvertent activation as well as unintentionally leaving the chip card in an unwanted switching state is also excluded. The building depth is very small and is therefore preferably suitable for chip cards. The manufacture may be performed within the required steps of manufacturing the card. No additional process steps are required in the manufacturing process. There is only a minor increase of the number of components on the chip card.
A preferred further embodiment of the chip card according to the invention has two capacitive switching elements which comprise touch zones formed with conductor structures, which with respect to their capacitance can be changed by means of a touch, and an associated evaluation circuit for detecting capacitance changes. Such conductor structures can be easily formed in a printed circuit board technique. The conductor structures should not be positioned unprotected on the upper surface of the chip card but may also be provided with a dirt-repelling and corrosion-resistant or destruction-inhibiting coating. However, when a mechanically unprotected arrangement of these conductor structures is chosen, its reliability of operation is not or at least not directly affected by dirt or corrosion. The conductor structures may also be arranged in a concealed form on the chip card so that the, for example, graphic configuration of the touch zones can be freely realized. This may simplify the ease of handling by the user.
Preferably, each conductor structure comprises at least two plane, interdigitally intertwined conductor configurations. Each conductor configuration is assigned to a row of strip-shaped conductor sections connected together in a conducting manner. Preferably, a conductor section of a first conductor configuration and a conductor section of a second conductor configuration are alternately situated substantially parallel to each other. An increase of the capacitance of the capacitive switching element is thereby achieved, and a larger change of this capacitance is realized upon a user""s touch. This alleviates the reliable detection of an operation.
In each conductor structure described hereinbefore, a first one of the conductor configurations constitutes an energizing electrode and the associated second one of the conductor configurations constitutes the relevant conductor structure of a measuring electrode. Each energizing electrode of the two capacitive switching elements is connected to one of the terminals of an antenna coil arranged on the chip card and used for the wireless transmission of the data signals. The energizing electrodes are thus directly fed by the electromagnetic field generated by or received from the antenna coil. A corresponding alternating voltage, which can be detected and processed in a simple way, is impressed on the measuring electrodes of the switching elements via the capacitances formed by the conductor structures. By touching the conductor structures in the touch zones, the capacitance of optionally one of the conductor structures can be changed. This change is also easily detectable and leads to a corresponding recognition of the user""s touch and hence the command given by this user. Moreover, combinations of touches of the touch zones are feasible. For said evaluations, the measuring electrodes are coupled to the evaluation circuit.
In a further embodiment of the invention, the measuring electrodes are constituted by a common conductor arrangement overlapping the two touch zones and comprising the corresponding conductor configurations. By virtue of such a conductor arrangement, the implementation of the measuring electrode as a common conductor structure and hence the process of manufacturing of the chip card is simplified.
For a simplified manufacture of a chip card of the type according to the invention, the switching element(s) together with the data-processing circuit is (are) arranged on a common supporting element. Preferably, the arrangement on this common supporting element also comprises terminals for the previously mentioned antenna coil. The supporting element with the elements arranged thereon may then be pre-manufactured as a module which, in a final manufacturing step, can be composed, for example, welded together with the antenna coil and possible further components of the chip card in the body of the card.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.